Transmission apparatus and transmission method

ABSTRACT

A transmission apparatus capable of preventing both degrading of the error rate characteristic and deterioration of throughput caused by repeated retransmissions. In the apparatus, arrangement determination section  103  determines in an initial transmission to perform general constellation mapping, and determines in a retransmission to vary a constellation mapping position or vary a bit arrangement of each symbol according to the number of retransmissions. Data interchanging section  105  interchanges transmission data for each bit on a symbol basis to be in a bit arrangement determined by arrangement determining section  103 . Mapper section  106  configures (maps) the transmission data input from data interchanging section  105  in each symbol to be mapped in the constellation mapping position determined in arrangement determining section  103.

TECHNICAL FIELD

The present invention relates to a transmission apparatus andtransmission method for performing retransmission of erroneous data.

BACKGROUND ART

The technique conventionally used in communication systems havingchannel conditions with low reliability and varying with time is toperform error correction based on an Automatic Repeat Request (ARQ)system and Forward Error Correction (FEC) technique, and called hybridARQ (HARQ). When an error is detected by well-used Cyclic RedundancyCheck (CRC) , a receiving section in the communication system requests atransmitting section to retransmit a data packet that is erroneouslyreceived (for example, Non-patent Document 1 and Non-patent Document 2).

DISCLOSURE OF INVENTION

The ARQ system includes three different types, types I to III.

Type I is a scheme where a received packet containing an error isdiscarded, a new copy of the same packet is separately retransmitted anddecoded, and previous and new packets received are not combined.

Type II is a scheme where a received packet containing an error is notdiscarded, and combined with an additionally retransmitted packet, anddecoding is continuously performed. The retransmitted packet has arelatively high coding rate (coding gain), and is sometimes combinedwith stored soft-information obtained from previous transmission in areceiving section.

Type III is almost the same as aforementioned type II, and a schemewhere each retransmitted packet can automatically be decoded. This meansthat a transmitted packet can be decoded without being combined with aprevious packet, and such a scheme is useful when part of a packet is sodamaged that the information can hardly be reused.

FIG. 1 is a diagram illustrating mapping of each symbol in an 8PSKmodulation scheme. In 8PSK, since eight mapping positions exist in theIQ plane, three bits can be included and transmitted in a single symbol.In each symbol, a most significant bit a1 is a first bit, bit a2 next tothe most significant bit a1 is a second bit, and a least significant bita3 is a third bit.

-   [Non-patent Document 1] S. Kallel, “Analysis of a type II hybrid ARQ    scheme with code combining”, IEEE Transactions on Communications,    Vol. 38, No. 8, August 1990-   [Non-patent Document 2] S. Kallel, R. Link, S. Bakhtiyari,    “Throughput performance of Memory ARQ schemes”, IEEE Transactions on    Vehicular Technology, Vol. 48, No. 3, May 1999

DISCLOSURE OF INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION

In the conventional transmission apparatus and transmission method,retransmission data of each symbol is retransmitted in the samepropagation path as that in the first transmission, and such a problemarises that an error occurs in the same data repeatedly. Then, when anerror occurs in the same data repeatedly, the retransmission isrepeated, which results in another problem that the throughputdeteriorates.

Further, in the conventional transmission apparatus and transmissionmethod, in each symbol, decision regions of the first and second bitsare different from a decision region of the third bit, and error ratecharacteristics are thus different between the first and second bits andthird bit, resulting in another problem that the error ratecharacteristic of the third bit degrades.

FIGS. 2 to 4 are diagrams showing the decision regions respectively forbits a1 to a3. FIG. 2 is a diagram showing a decision region of thefirst bit, and the first bit can be decided using a line with an angleof 22.5 degrees from the I axis as threshold #10. In other words,section 1 above threshold #10 is a decision region for “0”, whilesection 2 under threshold #10 is a decision region for “1”.

FIG. 3 is a diagram showing a decision region of the second bit, and thesecond bit can be decided using a line with an angle of 67.5 degreesfrom the I axis as threshold #11. In other words, section 1 underthreshold #11 is a decision region for “0”, while section 2 abovethreshold #11 is a decision region for “1”.

FIG. 4 is a diagram showing a decision region of the third bit, and thethird bit can be decided using thresholds #12 and #13. In other words,section 1 that is under threshold #12 and above threshold #13 is adecision region for “0”, section 2 that is above threshold #12 and abovethreshold #13 is a decision region for “1”, section 3 that is abovethreshold #12 and under threshold #13 is a decision region for “0”, andsection 4 that is under threshold #12 and under threshold #13 is adecision region for “1”.

It is understood from FIGS. 2 to 4 that two decision regions exist foreach of the first and second bits, while four regions exist for thethird bit. Accordingly, a Euclidean distance between decision regionsfor “0” and “1” in the third bit is smaller than a Euclidean distancebetween decision regions for “0” and “1” in each of the first and secondbits, and a problem arises that the third bit tends to be erroneouseasier than the first and second bits. When an error occurs in the thirdbit, a method of retransmitting the data is considered, but the errorrate characteristic of the third bit of the retransmission data stillhas a higher possibility of degradation than that of the first andsecond bits, resulting in a problem that the throughput deteriorates byrepeating retransmissions.

It is an object of the present invention to provide a transmissionapparatus and transmission method capable of preventing degrading of theerror rate characteristic and further preventing deterioration ofthroughput caused by repeated retransmissions.

MEANS FOR SOLVING THE PROBLEM

A transmission apparatus of the present invention adopts a configurationprovided with an arrangement determiner that determines a constellationmapping position indicating an arrangement position of each symbol datain the IQ plane when transmission data is retransmitted so that theconstellation mapping position becomes different from that in a lasttransmission, a data assigner that assigns transmission data to eachsymbol so that each symbol data with the same amplitude is arranged inthe constellation mapping position determined by the arrangementdeterminer, and a transmitter that transmits the transmission data thatis assigned to each symbol by the data assigner.

Further, a transmission apparatus of the invention adopts aconfiguration provided with a data interchanger that interchangespredetermined bits of transmission data so that a bit arrangement ofeach symbol, when the transmission data is retransmitted, becomesdifferent from that in a last transmission, a data assigner that assignsthe transmission data interchanged by the data interchanger to eachsymbol so that each of a plurality of items of symbol data with the sameamplitude is arranged in a constellation mapping position indicating anarrangement position of each symbol of the transmission data in the IQplane, and a transmitter that transmits the transmission data that isassigned to each symbol by the data assigner.

A transmission method of the invention has the steps of determining aconstellation mapping position indicating an arrangement position ofeach symbol in the IQ plane when transmission data is retransmitted sothat the constellation mapping position in retransmitting transmissiondata becomes different from that in a last transmission, assigningtransmission data to each symbol so that each symbol data is arranged inthe determined constellation mapping position, and transmitting thetransmission data assigned to each symbol.

ADVANTAGEOUS EFFECT OF THE INVENTION

According to the invention, it is possible to prevent the error ratecharacteristic from degrading, while further preventing deterioration ofthe throughput caused by repeated retransmissions.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram showing conventional constellation mapping;

FIG. 2 is another diagram showing the conventional constellationmapping;

FIG. 3 is another diagram showing the conventional constellationmapping;

FIG. 4 is still another diagram showing the conventional constellationmapping;

FIG. 5 is a block diagram illustrating a configuration of acommunication system according to an Embodiment of the invention;

FIG. 6 shows a table storing rule selection information according to theEmbodiment of the invention;

FIG. 7 is a diagram showing constellation mapping according to theEmbodiment of the invention;

FIG. 8 is another diagram showing the constellation mapping according tothe Embodiment of the invention;

FIG. 9 is another diagram showing the constellation mapping according tothe Embodiment of the invention;

FIG. 10 is another diagram showing the constellation mapping accordingto the Embodiment of the invention;

FIG. 11 is another diagram showing the constellation mapping accordingto the Embodiment of the invention;

FIG. 12 is another diagram showing the constellation mapping accordingto the Embodiment of the invention;

FIG. 13 is another diagram showing the constellation mapping accordingto the Embodiment of the invention;

FIG. 14 is another diagram showing the constellation mapping accordingto the Embodiment of the invention; and

FIG. 15 is still another diagram showing the constellation mappingaccording to the Embodiment of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

An Embodiment of the invention will specifically be described below withreference to accompanying drawings.

Embodiment

FIG. 5 is a block diagram illustrating a configuration of communicationsystem 100 according to an embodiment of the invention. Transmissionapparatus 101 is configured with arrangement determining section 103,interleaver 104, data interchanging section 105, mapper section 106, andmodulation section 107. Reception apparatus 102 is configured witharrangement judging section 109, demodulation section 110, demappersection 111, data interchanging section 112 and deinterleaver 113.

From number-of-transmission information, arrangement determining section103 determines in an initial transmission to perform generalconstellation mapping predetermined for each modulation scheme, anddetermines in a retransmission to vary whether a constellation mappingposition or a bit arrangement of each symbol according to the number ofretransmissions. Arrangement determining section 103 instructs mappersection 106 to vary a constellation mapping position when determining tovary the constellation mapping position, while instructing datainterchanging section 105 to vary a bit arrangement when determining tovary the bit arrangement.

Interleaver 104 rearranges transmission data for each bit and outputs todata interchanging section 105. Data interchanging section 105interchanges the transmission data input from interleaver 104 for eachbit on a symbol basis (one symbol contains three bits in 8PSK) so as tobe arranged in the bit arrangement determined by arrangement determiningsection 103 in accordance with the instruction of arrangementdetermining section 103. In case of 8PSK, data interchanging section 105performs processing of dividing a data sequence for each symbol so thatone symbol contains three bits, and subsequently, performs interchangingprocessing for each bit on each symbol. Then, data interchanging section105 outputs the transmission data interchanged for each bit to mappersection 106. When arrangement determining section 103 determines only tovary a constellation mapping position of symbol data, i.e. when datainterchanging section 105 is not instructed from arrangement determiningsection 103, the transmission data input from interleaver 104 is outputfrom data interchanging section 105 to mapper section 106 without anyprocessing. A method for interchanging transmission data for each bitwill be described later.

Mapper section 106 that is a data assigner, in accordance with theinstruction of arrangement determining section, configures (maps) thetransmission data input from data interchanging section 105 in eachsymbol so as to be mapped in the constellation mapping positiondetermined by arrangement determining section 103. Mapper section 106outputs the transmission data configured in each symbol to modulationsection 107. Meanwhile, when not instructed anything from arrangementdetermining section 103, mapper section 106 configures the transmissiondata in each symbol so as to be mapped in a general constellationmapping position predetermined for each modulation scheme. In addition,a method will be described later for varying the constellation mappingposition of each symbol data.

Modulation section 107 modulates the transmission data input from mappersection 106 with a predetermined modulation scheme and outputs tochannel 108. In addition, when transmission data is transmitted by radiosignal, the transmission data output from modulation section 107 is upconverted from a baseband frequency to radio frequency and transmittedfrom an antenna via a radio communication channel.

Channel 108 is generally a radio communication channel and transmits thetransmission data transmitted from transmission apparatus 101 toreception apparatus 102.

Arrangement judging section 109 knows the constellation mapping positionor bit arrangement corresponding to the number-of-transmissioninformation shared with arrangement determining section 103. Then,arrangement judging section 109 does not output anything in an initialreception, and when receiving retransmitted data, generates restorationinformation to restore the constellation mapping position of thereceived data to a general constellation mapping position correspondingto the number-of-transmission information, and outputs the generatedrestoration information to data interchanging section 112 or demappersection 111. More specifically, when arrangement judging sectionreceives the data where a bit arrangement of each symbol is varied, therestoration information is output to data interchanging section 112,while when receives the data where a constellation mapping position ofeach symbol data is varied, the restoration information is output todemapper section 111.

Demodulation section 110 demodulates the received data to output todemapper section 111. More specifically, demodulation section 110configures (maps) the received data in the constellation mappingposition for each bit, and decides “1” and “0” of the received data foreach bit using a threshold based on the constellation mapping positionwhere the data is mapped.

According to the restoration information input from arrangement judgingsection 109, with respect to the received data input from demodulationsection 110, demapper section 111 re-configures the transmission data soas to be arranged in the general constellation mapping position, andobtains a predetermined reception data sequence to output to datainterchanging section 112. Meanwhile, when the restoration informationis not input from arrangement judging section 109, demapper section 111obtains a predetermined reception data sequence without re-placing thetransmission data and outputs to data interchanging section 112.

According to the restoration information input from arrangement judgingsection 109, data interchanging section 112 interchanges each bit datafor each symbol data with respect to the received data input fromdemapper section 111. Then, data interchanging section 112 outputs thereceived data interchanged for each bit to deinterleaver 113. Inaddition, when receiving the data where only the constellation mappingposition of symbol data is varied, i.e. not receiving anything fromarrangement judging section 109, data interchanging section 112 outputsthe received data input from demapper section 111 to deinterleaver 113without any processing.

Deinterleaver 113 rearranges the received data input from datainterchanging section 112 and obtains reception data.

With reference to FIGS. 6 to 15, a method will be described below forvarying the constellation mapping position in the 8PSK modulationscheme.

Arrangement determining section 103 holds a rule table that stores ruleselection information as shown in FIG. 6, and selects a rule tointerchange data by using the number-of-transmission information andreferring to the rule table.

When the number of transmissions is one (in an initial transmission thatis not a retransmission), arrangement determining section 103 determinesConstellation 1 that is a constellation pattern to map in generalconstellation mapping positions of 8PSK as shown in FIG. 1.

When the number of transmission is two (in a first retransmission),arrangement determining section 103 determines Constellation 2 as aconstellation pattern. More specifically, arrangement determiningsection 103 selects a SWAP method as a data interchanging rule of theconstellation pattern. The SWAP method includes three schemes as shownin FIGS. 7 to 9. In other words, as shown in FIG. 7, the first scheme isto interchange data of the first bit and data of the second bit in eachsymbol data. As shown in FIG. 8, the second scheme is to interchangedata of the second bit and data of the third bit in each symbol data. Asshown in FIG. 9, the third scheme is to interchange data of the firstbit and data of the third bit in each symbol data. Arrangementdetermining section 103 selects any one from among the three schemes.Interchange of the data to vary the bit arrangement as shown in FIGS. 7to 9 is performed in data interchanging section 105.

When the number of transmissions is three (in a second retransmission),arrangement determining section 103 determines Constellation 3 as aconstellation pattern. More specifically, arrangement determiningsection 103 selects an Inversion method as a data interchanging rule ofthe constellation pattern. As shown in FIG. 10, the Inversion method ischanging “0” that is data of the third bit to “1”, while changing “1”that is data of the third bit to “0”, in each symbol data. Interchangingthe data of the third bits by data interchanging section 105 makes itpossible to make these changes.

When the number of transmissions is four (in a third retransmission),arrangement determining section 103 determines Constellation 4 as aconstellation pattern. More specifically, arrangement determiningsection 103 selects a Rotational Shift method as a data interchangingrule of the constellation pattern. The Rotational Shift method has twoschemes as shown in FIGS. 11 and 12. In other words, as shown in FIG.11, the first scheme is to shift data of the first bit to the secondbit, shift data of the second bit to the third bit, and further shiftdata of the third bit to the first bit, in each symbol data. As shown inFIG. 12, the second scheme is to shift data of the first bit to thethird bit, shift data of the second to the first bit, and further shiftdata of the third bit to the second bit. Arrangement determining section103 selects either one from the two schemes. Interchange of the data tovary the bit arrangement as shown in FIGS. 11 and 12 is performed indata interchanging section 105.

When the number of transmission is five (in a fourth retransmission),arrangement determining section 103 determines Constellation 5 as aconstellation pattern. More specifically, arrangement determiningsection 103 selects a Radius Circle Shift method as a data interchangingrule of the constellation pattern. The Radius Circle Shift method hastwo schemes as shown in FIGS. 13 and 14. In other words, as shown inFIG. 13, the first scheme is to rotate each symbol data by two stepscounterclockwise in the IQ plane. In addition, one step means rotatingsome constellation mapping point to adjacent constellation mappingpoint. As shown in FIG. 14, the second scheme is to rotate each symboldata by four steps counterclockwise in the IQ plane. Arrangementdetermining section 103 selects either one from the two schemes. Thus,in the Radius Circle Shift method, by rotating the constellation mappingposition of each symbol along the circumference of a circle with anintersection point of the I axis and Q axis as a center in the IQ plane,the constellation mapping point is varied. Shift of each symbol data tovary to the constellation mapping point in FIGS.13 and 14 is performedin mapper section 106.

When the number of transmissions is six (in a fifth retransmission),arrangement determining section 103 determines Constellation 6 as aconstellation pattern. More specifically, arrangement determiningsection 103 selects a Rotational shift & Inversion method as a datainterchanging rule of the constellation pattern. As shown in FIG. 15,the Rotational Shift & Inversion method is to shift data of the firstbit to the second bit, shift data of the second bit to the third bit,and further shift data of the third bit to the first bit, in each symboldata, while changing “0” that is data of the first bit to “1”, andchanging “1” that is data of the first bit to “0”, in each shiftedsymbol data.

Interchange of the data to vary the bit arrangement as shown in FIG. 15is performed in data interchanging section 105.

In addition, in the 8PSK modulation scheme, each symbol data has thesame amplitude, and an error of each bit is caused by a difference inphase decision region. Meanwhile, in the 16QAM modulation scheme, thephase and amplitude differ between symbol data, and an error of each bitis caused by a difference in amplitude decision region in addition tothe difference in phase decision region.

Thus, according to this Embodiment, since the bit arrangement in eachsymbol is varied corresponding to the number of retransmissions, aparticular bit of each symbol can be prevented from being erroneousrepeatedly, and it is thereby possible to prevent the error ratecharacteristic from degrading and further prevent deterioration of thethroughput caused by repeated retransmissions. Further, according tothis Embodiment, in the 8PSK modulation scheme where each symbol datahas the same amplitude, by simple processing for rotating a phase ofeach symbol by two steps or four steps, or for varying the bitarrangement in each symbol, it is possible to prevent a particular bitof each symbol from being erroneous repeatedly. Furthermore, accordingto this Embodiment, in the 8PSK modulation scheme including the sameamplitude, when data is retransmitted, each symbol is mapped in aconstellation mapping position where the phase is rotated by two stepsor four steps, and it is thus possible to transmit each symbol data viaa different propagation path corresponding to the number ofretransmissions. The effect by fading thus differs corresponding to thenumber of retransmissions, thereby enabling the time-space diversityeffect to be produced, and it is possible to prevent an error fromconcentrating on particular symbol data.

In addition, in the above-mentioned Embodiment, a constellation mappingposition of transmission data is varied in the 8PSK modulation scheme.However, the invention is not limited thereto, and is applicable tomodulation schemes such as 16PSK, 32PSK, 64PSK and the like where eachsymbol data has the same amplitude. Further, in the above-mentionedEmbodiment, symbol data is rotated by two steps or four steps in theRadius Circle Shift method, but not limited thereto, and may be rotatedby any steps such as three steps and the like as well as two steps andfour steps. Transmission apparatus 101 and reception apparatus 102 ofthe above-mentioned Embodiment are applicable to a base stationapparatus and/or communication terminal apparatus. Further, in theabove-mentioned Embodiment, the constellation mapping point is variedusing either one of the SWAP, Inversion, Rotational Shift and RadiusCircle Shift methods, but the invention is not limited thereto. Theconstellation mapping position may be varied in any combinations of theSWAP, Inversion, Rotational Shift and Radius Circle Shift methods.Moreover, in the above-mentioned Embodiment, the number of transmissionsis associated with the data interchanging rule as shown in FIG. 6.However, the invention is not limited thereto, and association of thenumber of transmissions and data interchanging rule may be changedflexibly.

The present application is based on Japanese Patent Application No.2003-341718 filed on Sep. 30, 2003, entire content of which is expresslyincorporated by reference herein.

INDUSTRIAL APPLICABILITY

The present invention is suitable for use in a transmission apparatusand transmission method for performing retransmission of erroneous data.

1. A transmission apparatus comprising: an arrangement determiner thatdetermines a constellation mapping position indicating an arrangementposition of each symbol data in the IQ plane when transmission data isretransmitted so that the constellation mapping position becomesdifferent from that in a last transmission; a data assigner that assignstransmission data to each symbol so that the each symbol data with thesame amplitude is arranged in the constellation mapping positiondetermined by the arrangement determiner; and a transmitter thattransmits the transmission data that is assigned to the each symbol inthe data assigner.
 2. The transmission apparatus according to claim 1,wherein the arrangement determiner rotates the constellation mappingposition of the last transmission by predetermined angles along acircumference of a circle with an intersection point of the I axis and Qaxis as a center in the IQ plane to determine as the constellationmapping point when the transmission data is retransmitted.
 3. Thetransmission apparatus according to claim 1, further comprising: a datainterchanger that interchanges predetermined bits of the transmissiondata so that a bit arrangement of each symbol when the transmission datais retransmitted becomes different from that in the last transmission,wherein the data assigner assigns the transmission data interchanged inthe data interchanger to each symbol.
 4. A transmission apparatuscomprising: a data interchanger that interchanges predetermined bits oftransmission data so that a bit arrangement of each symbol when thetransmission data is retransmitted becomes different from that in a lasttransmission; a data assigner that assigns the transmission datainterchanged by the data interchanger to each symbol so that each of aplurality of items of symbol data with the same amplitude is arranged ina constellation mapping position indicating an arrangement position ofeach symbol of the transmission data in the IQ plane; and a transmitterthat transmits the transmission data that is assigned to the each symbolby the data assigner.
 5. A base station apparatus having a transmissionapparatus, wherein the transmission apparatus comprising: an arrangementdeterminer that determines a constellation mapping position indicatingan arrangement position of each symbol data in the IQ plane whentransmission data is retransmitted so that the constellation mappingposition becomes different from that in a last transmission; a dataassigner that assigns transmission data to each symbol so that the eachsymbol data with the same amplitude is arranged in the constellationmapping position determined by the arrangement determiner; and atransmitter that transmits the transmission data that is assigned to theeach symbol by the data assigner.
 6. A communication terminal apparatushaving a transmission apparatus, wherein the transmission apparatuscomprising: an arrangement determiner that determines a constellationmapping position indicating an arrangement position of each symbol datain the IQ plane when transmission data is retransmitted so that theconstellation mapping position becomes different from that in a lasttransmission; a data assigner that assigns transmission data to eachsymbol so that the each symbol data with the same amplitude is arrangedin the constellation mapping position determined by the arrangementdeterminer; and a transmitter that transmits the transmission data thatis assigned to the each symbol by the data assigner.
 7. A transmissionmethod comprising the steps of: determining a constellation mappingposition indicating an arrangement position of each symbol in the IQplane when transmission data is retransmitted so that the constellationmapping position becomes different from that in a last transmission;assigning transmission data to the each symbol so that each symbol datais arranged in the determined constellation mapping position; andtransmitting the transmission data assigned to the each symbol.